There's just one little problem: Unlike what he captioned in the post, boxing isn't "just cardio." Cardio is that run through Hollywood you took with your buddies last week. Here's some tips for how the fitness buff can perfect his form:

Keep Your Gloves Up

This trainer is a really nice guy. Justin fails to protect his face after every hit, leaving himself wide open for a pop straight in the kisser. As a novice boxer, work on protecting that pretty face before perfecting your hook.

Extend Your Jab

I know you've got some power in that arm, JB. Use it! Don't keep that jab all tucked up. It's a powerful tool.

Power Through Your Cross And Hooks

A boxer's best weapon is a strong right hook. It's the knock-out punch. Try throwing your whole body into it and you'll quickly realize that boxing isn't just a cardio burn. And when you're shoe-shining hooks, keep your elbows up to drive more power from the shoulder.

To Justin's credit, he admits he's "not a boxer," but with so many friends in the game, he could have access to the best training partners out there. Call Floyd. The champ is bound to have a few tips.